A valve of this kind generally comprises a body in which there slides a valve head connected to an output pinion of a rotary motor via a device which converts a pivoting movement of a pinion, meshing with the output pinion, into a translational movement of a slide connected to the valve head and mounted so as to slide inside the body via a guide liner. The pinion is mounted so as to pivot relative to a slide mounting member comprising a tubular wall fixed inside the body. The tubular wall is provided with cam surfaces which each act on a follower roller mounted on a mounting part. The latter is on the one hand rotated by an eccentric fork connected in rotation to the pinion, and on the other hand is mounted so as to pivot on one end of the slide. The mounting part is thus driven rotationally by the pinion, causing the rollers to move along the cam surfaces, which are designed to bring about a translational movement of the mounting part which in turn carries with it the slide and the valve head.
The pinion is connected to one end of a spindle whose other end is connected to the rotary drive fork of the mounting part. The spindle is mounted pivotally in a rotary guide liner force-fitted into a plate fixed to the body. Correct operation and long life of the valve and of the conversion device require accurate relative positioning of the body, the valve head, the tubular wall, the plate, the guide liners, the spindle, the pinion and the fork otherwise there will be premature wear of all or some of these components. Achieving the requisite positioning accuracy makes the assembly and machining of the components relative expensive.